PLC Basics Handbook
A four-page document for engineers new to automation, panel technicians and maintenance staff who need to read, wire and check PLC I/O. Five parts follow the signal path. Scan cycle: the four steps of one scan and five things to design around it (short pulses, timers, program order, restart, watchdog). Inputs: PNP versus NPN, compatible input modules and the COM terminal, a five-step procedure for wiring a 24VDC input, and common wiring mistakes. Outputs: relay versus transistor by load type, speed, life and leakage current; four questions about the load before choosing an output; surge suppression by load type. Timers and counters: four timer types, TON, TOF and TP behaviour, four things to define for a counter, and common mistakes. Analog signals: 0–10V, 0–20mA, 4–20mA and ±10V compared; 2-, 3- and 4-wire transmitters; the scaling formula with a 4–20mA to 0–10 bar example; wiring and noise. Five checklist groups A–E to tick during commissioning. Content is drawn from articles #32–#36 of the MINATA Learn Automation series; instruction names, scan times, current per point and raw ranges follow the PLC maker's documentation.
What is inside
- The four steps of a scan cycle
- Five things to design around the scan
- PNP and NPN inputs, the COM terminal
- Wiring a 24VDC input step by step
- Relay and transistor outputs, surge suppression
- TON, TOF, TP timers and counters
- 0–10V and 4–20mA signals, 2/3/4-wire transmitters
- Analog scaling formula with an example
- Five commissioning checklist groups A–E
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